This invention relates to composite mirror panels and the manufacture of composite mirror panels.
Composite mirror panels are useful for many purposes and an increasing use is being found in the field of solar energy collectors.
In one form of solar energy transducing installation, mirrors are held on supports distributed around a field. Each support may carry mirrors several square meters in area and there may for example be a hundred or more supports distributed around a field up to a few hectares in area. All the mirrors are arranged to reflect solar energy onto for example an energy collecting surface of a steam generator arranged to drive a turbo-generator. So that the mirrors can continue to reflect sunlight onto the energy collecting surface as the sun moves across the sky, the mirror supports incorporate means for adjusting the orientations of the mirrors about vertical and horizontal axes. The combination of such a mirror and support is known as a heliostat. Such mirrors may be flat or curved.
The efficiency and cost of such a solar energy transducing installation will depend on a number of factors, inter alia, the properties of the heliostat mirrors.
It is clearly desirable that a solar mirror should have a high reflectivity, and that such reflectivity should be preserved against weathering to give the mirror a long useful life. It is also desirable that the mirror should be light in weight because a low inertia makes it easier to track the sun and the cost of the heliostat support can be reduced. However to ensure that the mirror is capable of continuously reflecting sunlight onto a collector surface the mirror must be substantially rigid. A heliostat mirror may, e.g. be located a hundred meters or more away from the collector, in which case even quite minor movement or deformation of the mirror due to wind gusts would deflect the reflected sunlight away from the collector surface.
Composite mirror panels which are light, rigid and weatherproof are also useful for other purposes, for example as building panels.
It is known to make mirror panels of foam sandwich construction but the methods of construction hitherto proposed do not enable product standards now often demanded, to be reliably met. In particular, problems arise in achieving a high optical and mechanical integrity of the composite structure together with accurate conformity with prescribed dimensional specifications.